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SMPS to run Gu50 heaters? Extra filtering?

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dubadub

dubadub

Member
Joined 2020
#1
Greetings Friends. I need a 12vDC power supply to heat 2x Gu50 tubes for an amp. While the Hammond 166L12 is one option, I'm curious about these small n cheap SMPS they got nowadays. Here's a SMPS on Ebay, 12V 2A. Gu50 need 0.8A per tube, so 2A should be plenty. Is this a viable option for powering tubes? Would a 6800uF 25V (audio grade) cap be useful across the outputs?

thanks for taking a look!

will
 
#2
Many SMPSs will not start up into a cold tube heater since a 1 amp heater may draw 3 to 4 amp for the first second after power up. Sticking a fat cap across the output makes things worse. I have been using 24 volt SMPSs turned up to (or as close as possible to) 26 volts to power 4 X 26HU5 tubes rated for 26 volts at 0.6A. Some 100 watt SMPS do not always start up. A Meanwell 150 watt unit works fine. I have not seen a need for any filtering, but the SMPS only powers the output tubes.
 
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#3
I would buy something from a reputable company like Meanwell. You’ll get a legitimate datasheet with surge and ripple ratings. The ripple will be low but if you want decrease it further add a choke input filter. You won’t need much, say 100uh and then a low esr cap. 1000uf would be more than enough.
 
#5
You need an oversized smps, to be able to handle the cold heater current. I use a 12V 13A one from AliExpress for 4x6P41S and a 12AT7, it does not break a sweat.
You could also get one from a reputable supplier, but still will need to be overrated.
 
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#6
I see. Gets to be cheaper to buy the Hammond transformer. I guess any 12vAC trafo would do, as long as it's quality. Wavebourn recommended DC supplies for all the tubes in that design. I've built linear supplies before... I'm picturing something like this, adjusting the dropping resistor to get happy:
Screenshot_20240703-153855.png

Does the transformer need to be over-rated for this?

Thanks!
 
#7
The Antek AS0506 Toroidal trafo ships from the U.S. and will provide 2A at 6.3V DC using 0.22 to 0.47Ω in the CRC.
SB1540-3G diodes run cooler, and are recommended.
This is a more reliable solution than offline-> DC boxes. The leakage current needs care with these also, and we are better off without broadband radiated/coupled emissions too, IMHO.
 
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#9
I think your on the edge with this 12V 3A would be what I would suggest. The SMPS you suggest does have main input filter. I not seen one without (except homebrew) as products cannot ship if don't meet EMC specs. They may also need air cooling. Certainly I used one for powering 4x6C33
 
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